1. Field
Embodiments relate to a method, apparatus, and medium for calibrating a compass sensor and calculating the quality of the calibration of the compass sensor and a distortion factor, and more particularly, to a method, apparatus, and medium for calibrating azimuth data acquired by a compass sensor and evaluating the quality and distortion of the calibrated azimuth data.
2. Description of the Related Art
Compass sensors have been widely used in various modern products. In particular, compass sensors have been adopted in a variety of transportation vehicles such as ships, planes, and automobiles as a tool for determining the heading direction of transportation vehicles. Also, compass sensors have been adopted in mobile robots that can autonomously travel from place to place as a tool for determining the traveling direction of mobile robots.
Compass sensors measure an inclination with respect to the due north of the Earth as an absolute azimuth by using an absolute coordinate system in which the due north of the Earth is regarded as one axis. Compass sensors can perform direction measurement due to minute magnetic fields that exist on the Earth.
Most compass sensors result in minor errors due to interference from a minor magnetic field. For example, assume that a compass sensor is installed in a mobile robot and that the mobile robot travels inside an apartment building. Various electronic products such as TVs, refrigerators, stereos, treadmills, and microwave ovens which can be used in an apartment building may affect a magnetic field in the apartment building. Since the Earth magnetism generates a weak magnetic field, data sensed by a compass sensor may be partially erroneous due to external magnetic interference with the compass sensor.
Therefore, in order to obtain precise azimuth data, data of a compass sensor needs to be calibrated. U.S. Pat. No. 4,414,753 discloses a technique of compensating a magnetometer which includes acquiring data with the aid of a magnetometer by rotating a vehicle 360 degrees; forming an ellipse based on the acquired data; transforming the ellipse into a circle; calculating a plurality of parameters regarding the ellipse and the circle; and compensating the magnetometer by performing hard iron compensation and soft iron compensation on the magnetometer using the parameters.
U.S. Pat. No. 5,828,984 discloses a technique of calibrating a compass sensor which involves acquiring elliptical trajectory data by rotating a compass sensor 360 degrees; determining the lengths of major and minor axes of the elliptical trajectory data and the angular deviation of the elliptical trajectory data from true magnetic north; and transforming the elliptical trajectory data into a circle by performing linear transformation according to the results of the determination.
Japanese Patent Laid-Open Gazette No. 1997-068431 discloses a technique of calibrating a compass sensor which involves fitting the output of a magnetic sensor to an ellipse and transforming the ellipse into a circle by calibrating a set of parameters regarding the ellipse.
The aforementioned conventional calibration techniques simply involve calibrating a compass sensor by transforming a geometrical figure obtained through simple fitting into a circle. In addition, no methods have yet been suggested to calibrate both data acquired by a compass sensor and an ellipse to which the acquired data is fit at the same time.
Moreover, in the aforementioned conventional compass sensor calibration techniques, data acquired by a compass sensor is fit to an ellipse, and then, the ellipse is readily transformed into a circle. Thus, it is impossible to determine whether a compass sensor has been properly calibrated and verify the reliability of data acquired by the compass sensor.